A great need exists for a relatively small device to determine the existence of an undesirable amount of specific gases in an atmospheric environment. For instance, the mining industry has a need to know when the levels of carbon dioxide or an explosive gas within a mine reach dangerous levels. Another area of concern is with respect to operators of closed vehicles such as aircraft and automobiles which are involved in an undetermined number of accidents resulting directly from the operators being overcome by carbon monoxide leaking from the engine exhaust systems into the operator compartments.
A number of devices are presently available which will identify gases in atmospheric environments but they are either expensive, bulky or relatively inaccurate. For instance, existing conductometric analyzers require bubbling of the gas stream being analyzed through a solution. This type of device requires a pump to force the gas sample through the solution and the devices are relatively heavy and not portable since they require power line connections or extremely heavy battery packs. Furthermore, they are not suitable for continuous monitoring under field conditions and are relatively expensive.
The known prior art conductometric gas analyzers mix the gas and water, remove gas bubbles from the water phase, and then pass the water containing the dissolved species over large conductometric electrodes. Gas and liquid flow rates are high and the apparatus required is heavy and bulky. Commercial conductometric analyzers presently on the market use flow rates as high as 1,000 milliliters of water per minute.
Another example of a gas detecting apparatus presently available is described in the patent issued to Schultze, U.S. Pat. No. 2,741,912 on "Apparatus for Detecting Gases or Vapors." This type of device is based on the principle that activated carbon increases in conductivity when exposed to harmful gases and vapors. Devices of this nature are subject to contamination build up and therefore do not provide an accurate indication of the instantaneous quality of the atmosphere being monitored.
G. Purt et al, U.S. Pat. No. 3,755,800 on "Automatic Fire Alarm Device" is exemplary of another approach to determining the presence of dangerous gases in an atmospheric environment. Devices such as Purt et al function on the principle that a catalytic reaction will occur when the dangerous gas contacts an anode in an electrolytic cell. The catalytic reaction causes an electrical current to be generated which may then be used to sound an alarm. Devices such as this are generally incapable of providing accurate measurements of the percentage of dangerous gas in the atmosphere and are only responsive to a limited number of elements.